Raw Water Cooling

Hello, I am looking for suggestions on what might be hanging up my raw water cooling system from flowing freely. The boat is new to me but built in the 70's and the previous owner says the water should be flowing a lot faster than what's happening, especially at higher RPM's. The engine is a DD 671 dry stacked, appears to not be over heating, and I have taken apart and cleaned the Raw Water Strainer, Heat Exchanger and replaced the impeller but still only a surge like flow. I was hoping some one could guide me on what to look at next. Thanks in advance for any suggestions. Trawler Forum has been a very positive experience and guide to my big boating success and look forward to reading it's contents nightly.

Joel Sparks

Joel check and make sure that you don't have a hose coming apart internally. You can also dive down and make sure that the water intake is not plugged with sea life or a plastic bag.

I assume there is a heat exchanger , clean it.

FF

Ditto FF here. We just had ours done (8V92s), and the difference was impressive. We actually took things one step further, and had all cooling systems serviced (oil, fuel, engine, intercoolers, etc.). It's amazing how gunked up they get over time.

Thanks guys but as I mentioned before I've cleaned the heat exchangers (engine & trans), cleaned the intake strainer and replaced the impeller. I had the boat out of the water for new bottom coat and checked the water intake, free & clear.

I was hoping their might be a common area elsewhere I should check or an insiders secret to getting the system clear. I think what's happened is some of the junk that I loosened from the heat exchanger got hung up deep in the system on an elbow or such and I probably should just go over the whole system and not be so lazy. That's what I'll do.

What kind of muffler do you have. Is it a water lift or straight through. I have the water lift on my John Deere and it surges also.

Joel - I know that this will sound silly but have you attempted to bleed air out of your system? I had this sort of problem but on a much smaller scale with our old sailboat where every time she came out for bottom paint etc the engine would run warmer than normal for weeks afterwards. Got smart one year and after she was back in the water I partially pulled the top water hose off the heat exchanger, which was the highest point in the system, and was suprized at the amount of air that came out before any water. Engine cooled fine after that and subsequent years I did the same thing immediately after her getting wet after a haul-out.
Just a thought.
By the way, where in Victoria are you - I'm out by the airport with my boat on the hard in the back yard.
John

Hey John, that's an interesting idea - Air in the System. I should take the hose off anyway to see if the problem is at the pump or after the exchanger. My boat is moored at Westport same spot since 1974. I, however, just acquired her after 2 years of friendly negotiations with the original owner. This weekend will be it's first real run in over a decade, going around Salt Spring Island, and I'm feeling prepared after doing all the proper fluid and filter changes and system checks. I'll look over the cooling again tomorrow and plan to leave Thursday. Thanks for your interest. I have alot to discuss with my new boat and it's updates.

Joel - great, Westport is where we had Penta for about 10 years until I pulled her and brought her home for a re-fit. Great marina, least it was when we left and now all I have to do is try and get back there next year - good luck I would say!
Cheers
John

You might think about having the fuel filtered if the boat's been sitting that long. Could be a lot of junk at the bottom of the tank(s) that will get good and stirred up for the first time in a long time.

Having a diver check and clean the out side the through hulls. Most hav a protective screen and it does no take much to restrict the flow.* I have a diver come every 6 moths to check/change the zincs and clean the though hulls, hull and prop of barnacles and growth

*
On the raw water side of the pump from the through hull to the pump the hose must be a non compressing wire enforced hose.* The reason is the pump is sucking which will tend to collapse of regular not wire enforced rubber hose. **On the engine side the hose can be a regular non wire enforced hose because the pump is blowing/pushing the water.

*

Check to see if your water heater is heated by the fresh water loop or the raw water loop. I know most boats nowadays are cooled be the freshwater loop, I did have a boat that was cooled by the raw water side of things and it did cause a problem when things got jammed up in there...I simply bypassed it(temporary fix) and the problem was solved.

Thanks everyone for your comments, I found the problem. Half way up the intake tube was partially blocked and one of the hoses was falling in on itself. All fixed and my trip around the Island was success and I ran her WOT for a good hour too with perfect temperature. The only problem I can see now is the cost of fuel.

Cost of fuel? Get an unlimited Boat/US towing policy and have them tow you around for free!

Joel, I hope you replaced the hose with a wire einforsed hose.* Otherwise it will collapse again.

On the raw water side of the pump from the through hull to the pump the hose must be a non compressing wire enforced hose.* The reason is the pump is sucking which will tend to collapse of regular not wire enforced rubber hose. **On the engine side the hose can be a regular non wire enforced hose because the pump is blowing/pushing the water.

regards

Phil/Fill

I know the problem has been long fixed, but the next time someone does a search for overheating problems, here's a couple more areas to check:

1. If a pump impeller failed in the past, did you find all the pieces? Prime areas to check are inlet side of fuel coolers and other heat exchangers. Look into the heat exchanger tubes; pieces of vane seem to be just the right size to get in there.

2. There is probably a grid on the outside of the hull protecting the raw water intake from ingesting twigs etc. The holes in this grid get progressively smaller with each layer of antifouling applied. The result is overtemp at WOT when the holes get small enough.

Mike

In cases such as you describe, I have found two culprits.

Hoses suffering from internal delamination an/or calcium build up. My recommendation is that hoses should be changed every 5 years.

Rubbish build up in the hosing between the impeller and the exchanger or intercooler. This happens when an impeller has broken up and the bits have travelled downstream.

Hope this helps.

" If a pump impeller failed in the past, did you find all the pieces?"

For a cruiser this is an ongoing hassle as pump failure is almost inevitable.
Esp in brown water with sand and silt .

Our solution for the offshore boats we built was a large Sen Dure "Y" strainer AFTER the impeller water pump.

IF there are loose pieces (even heavy dust) , there all caught in an EZ to clean strainer.

Today the Dry Stack & keel cooling is a better choice for a newbuild.

Far less danger and maint.